1. Technical Field
The present invention relates to an image processing apparatus equipped with a moving picture decoding function and a drawing function for displaying image data, which are the decoding results, on a display screen.
2. Background Art
A variety of image processing apparatuses are known, which are capable of storing compression encoded data ob a moving picture obtained through compression algorithm such as MPEG (Moving Picture Expert Group) and decoding the compression encoded data to thereby display image data, which are the decoding results, on a display device. In such a kind of image processing apparatus, the display device displays the image data at a rate of one frame per one vertical scanning in synchronism with a vertical scanning period, which is a constant time length. To the contrary, the required time for the decoding process to acquire one-frame image data from the compression encoded data is uneven between frames. Moreover, if the processing capability of a decoder performing the decoding process is insufficient, the decoding process is out of synchronism with the vertical scanning period, which is an image display period, and therefore, a problem occurs in that the frame on which the decoding process was out of synchronism is erroneously displayed on a display device.
As a technical means for solving such a problem, for example, one disclosed in Patent Document JP-A-2000-232649 is known. An MPEG video decoder disclosed in Patent Document JP-A-2000-232649 includes a picture decoding section, a decoding start command generating section, a decoding frame buffer, and a picture data output section. Here, the picture decoding section starts decoding of a MPEG bit-stream for a predetermined number of pictures (synonymous with the “frame”) in response to a decoding start command, and outputs a decoding completion notification when the decoding of the bit-stream for the predetermined number of pictures is completed. The decoding frame buffer sequentially stores picture data decoded by the picture decoding section, and outputs a buffer-full notification when a predetermined quantity of picture data (synonymous with the “image data”) are stored. The decoding start command generating section outputs the decoding start command when the decoding completion notification is output from the picture decoding section and the buffer-full notification is not output from the decoding frame buffer. The picture data output section transmits the picture data stored in the decoding frame buffer to the display device.
According to the MPEG video decoder, the picture decoding section continues the decoding process of the MPEG bit-stream asynchronous with the operation of the display device until the buffer-full notification is output from the decoding frame buffer, and the picture data, which are the decoding results, are sequentially stored in the decoding frame buffer, whereby the picture data output section can transmit the picture data stored in the decoding frame buffer to the display device. Therefore, the problem that the decoding process on some of the pictures is out of synchronism and the pictures are erroneously displayed on the display device can be resolved.
In an image processing apparatus which is used in a game machine such as a Pachinko machine, however, in order to enhance the presentation effect at the time of reproducing moving pictures along with sound effects, there is required a function of freely controlling a display start time of the display device starting the display of the moving pictures. However, in the prior art as disclosed in Patent Document JP-A-2000-232649, although the decoding process on the compression encoded data can be performed in asynchronism with the vertical scanning of the display device, the image data, which are the decoding results, are displayed on the display device when it comes to their turn in the decoding frame buffer. Therefore, there is a problem that it is difficult to freely control the time at which the image data, which are the decoding results, are displayed on the display device.